1. Field of the Invention
The present invention relates in general to a method and apparatus for placing a casing string in a well and, in particular, to an apparatus and method for gripping a pipe element from a top drive.
2. Brief Description of Related Art
During drilling of an oil and gas well, the wellbore is typically lined with tubular members, i.e., casing. Casing maintains the drilled wellbore opening and allows for the passage of tools, drilling fluids, drilled material, and produced hydrocarbons into and out of the wellbore. Casing is assembled in a process that involves lowering a portion of casing into the wellbore, gripping the casing through use of a pipe slips or an elevator, and maintaining the casing position while a separate elevator brings a new section of casing to the gripped portion, connects the new portion, and then lowers the combined sections further into the well. When the newly connected casing is substantially in the wellbore, the process repeats. This can be a time consuming and dangerous process as it can place workers in precariously high places in order to facilitate the connection of additional casing, and in areas where they may be prone to being struck by the moving casing elements.
In an effort to reduce the risks associated with running in casing strings, some systems utilize a top drive to both drill the wellbore and run casing. Top drive systems utilize a high horsepower motor and gearbox mounted to the drilling derrick axially above and in line with the wellbore. Top drives can move axially as needed to conduct drilling operations, and be shifted horizontally to a limited degree. When used to run casing, a hydraulically actuated casing gripper may be coupled to the top drive such that the top drive may variably raise and lower the casing gripper as needed to first secure a separate casing element and then couple that casing element to the casing string. Due to the nature of the design of the hydraulic systems of the casing gripper, the casing gripper causes the length of the casing drive system stack to be quite large. The length of these systems prevents the use of hydraulically actuated casing grippers in smaller drilling rigs that typically run casing that is only 4.5″ to 5.5″ in diameter. These smaller rigs have shorter masts, or are sometimes converted rigs that added a top drive system. In those rigs, a hydraulic casing gripper may be too long to fit into the drilling rig.
Attempts have been made to address some issues with hydraulically actuated gripping devices by removing the hydraulic elements and replacing them with a mechanically actuated system. These mechanically actuated devices generally rely on complicated systems that variably engage and disengage a series of cams and hooks that must transition between setting modes and torque modes where the nuts variably engage or disengage the gripping mechanism. Increased complexity often leads to an increased rate of failure as there are more moving pieces that can fail and cause the gripping device to cease functioning. Furthermore, these devices often utilize elastomeric elements that are compressed into engagement with an interior diameter of a casing member. These elastomeric elements are prone to wear and failure after repeated uses, increasing the downtime of the gripping device for maintenance and repair. Oftentimes, these devices also require significant operator preparation time to ensure that the particular device is suited for the particular type of casing or tubular member to be gripped. Other mechanically actuated systems grip casing by first stabbing a gripping tool into a casing element. A weight is then set on the casing element to hold the casing element stationary while the gripping tool actuates to grip the casing element. If the frictional force between the weight and the casing element is not sufficiently high, the tool will rotate within the casing element will rotate with the tool prior to tool actuation, thus preventing the gripping tool from actuating and gripping the casing.